鄂尔多斯盆地长北气田山西组2段高分辨率层序构型与砂体预测

The Sequence Architecture and Sandbody Predicition of the Second Member of Shanxi Formation in Changbei Gas Field,Ordos Basin

以钻井测井、岩芯描述和样品分析为基础,高分辨率层序分析为技术方法对鄂尔多斯盆地长北气田山西组2段进行了精细的沉积相和层序分析,将山2段确定为海相辫状河三角洲沉积体系,并将其划分为1个长期、2个中期、4个短期和9个超短期基准面旋回层序和2大类5种基准面旋回结构类型。分析了不同级别基准面旋回层序的叠加式样与砂体展布和演化规律,建立了以中期基准面升、降半旋回相域为等时地层单元的山2段地层格架和对单砂层进行了等时追踪对比,确定中期上升期是三角洲河道砂体连续叠置形成巨厚砂体的最有利时期,洪泛期为细粒沉积物沉积期,也是隔层和局域性盖层主要发育期,下降期受侵蚀影响河道砂体不发育。以高分辨率层序分析为基础,建立等时地层格架为约束条件,结合单砂体为等时地层单元编制砂岩等厚图、砂/泥比等值线图和沉积微相图,对长北气田山2段砂体分布开展序贯指示三维模拟和预测,为长北气田山2段气藏高效开发提供依据。

On the basis of integrated study of core description, well logging and sample analysis, the sedimentary facies and sequences of the Member 2 of the Shanxi Formation are analyzed thoroughly with the application of high-resolution sequence stratigraphy. The Member 2 of the Shanxi Formation is composed of a sedimentary system of marine braided fiver delta and can be divided into one long term, two middle terms, four short terms, nine super-short terms base-level cycle sequences, and two categories and five kinds of texture of base-level cycles. The stacking patterns and distribution and evolution of sandbodies at different orders of base-level cycles are studied in detail. The chronological stratigraphic units established on the basis of ascending and descending hemicycles of the medium term are used to trace and correlate the sandbodies in the Member 2 of the Shanxi Formation. It is indicated that the continuous stacking thick sandbodies in the delta channel developed at the ascending hemicycle and the fine-grained sediments deposited at the descending hemicycle which was the main development stage of regional restraining barrier and caprock. Based on above analysis and application of high-resolution sequence stratigraphy the isopach map of sandstone and ratio of sandstone to mudstone, the sedimentary mierofacies map and 3-D simulation of sequence indicator of sandbodies distribution were plotted in a chronological stratigraphic framework which provides reliable evidence for the prediction and evaluation of favorable sandbodies of the Member 2 of the Shanxi Formation in the Changbei Gas Field